This application claims priority to Japanese patent application serial number 2002-083755, the contents of which are incorporated herein by reference.
1. Technical Field
The present invention relates to piston-cylinder mechanisms. In particular, the present invention relates to piston-cylinder mechanisms that can be suitably utilized for pressure control units that are configured to control the pressure of a fluid, e.g., a hydraulic fluid, that is supplied from a plurality of sources of pressurized fluid to a plurality of external devices.
2. Description of the Related Art
A pressure control unit is known that is adapted to receive a supply of pressurized fluid from a plurality of sources of pressurized fluid for the purpose of fail safe. For example, each source of pressurized fluid includes a pressure generator and a pressure control valve. The pressure generator may produce a flow of highly pressurized fluid. In another know technique, hydraulic master cylinders are used as the sources of pressurized fluid. The sources of pressurized fluid are connected to external devices, e.g., vehicle wheel brakes, via the pressure control unit. The external devices are divided into a plural number of groups that correspond to the number of the sources of pressurized fluid. The pressure control unit is configured to have hydraulic circuits each connected to each group of the external devices. Therefore, even in case that one or more of the sources of pressurized fluid has failed to supply the pressurized fluid due to any trouble, the remaining source(s) of pressurized fluid still can supply the pressurized fluid to the corresponding group(s) of the external devices.
Nevertheless, there has been a problem that the number of the properly operable external devices will be reduced. For example, if the external devices are wheel brakes, braking forces applied to the wheels may be reduced.
It is accordingly an object of the present invention to teach improved techniques for reliably supplying pressurized fluid to a plurality of external devices even if any of sources of pressurized fluid has failed to supply the pressurized fluid.
According to one aspect of the present teachings, piston-cylinder mechanisms are taught that has a cylinder and a plurality of pistons. The pistons may be disposed within the cylinder in order to define a plurality of pressure chambers.
A plurality of individual sources of pressurized fluid (e.g., hydraulic pressure generators) and a plurality of individual external devices (e.g., wheel brake devices of vehicles) may be connected to the cylinder.
Each of the pressure chambers may communicate with one of the sources of pressurized fluid and/or one of the external devices that are connected to the cylinder, so that each piston may move in response to difference in pressure between the pressure chambers on both sides of the piston. Therefore, the pressure chambers may have substantially the same pressure with each other.
A valve may be associated with the pressure chamber(s) that communicates both the external device and the source of the pressurized fluid. The valve may open and close in response to the relative movement of the pistons that define the pressure chamber, with which the valve is associated. Preferably, the valve may open and close when the pressure chamber in question is expanded and contracted, respectively. Therefore, even when the source of pressurized fluid communicating with the pressure chamber in question has failed to supply the pressurized fluid for some reason or other, that pressure chamber still can be pressurized to deliver the pressurized fluid to the corresponding external device.
On the other hand, when the source of the pressurized fluid communicating only with the corresponding external device has failed to supply the pressurized fluid for some reason or other, the pressure chamber in question also still can be pressurized due to the relative movement of the pistons that define the pressure chamber in question.
Therefore, even if any of the sources of the pressurized fluid has failed to supply the pressurized fluid, the pressurized fluid can be delivered to all of the external devices as long as any one of the sources of the pressurized fluid properly operates to supply the pressurized fluid.
According to another aspect of the present teachings, pressure control units are taught that may include the piston-cylinder mechanism. The pressure control units also may include a plurality of vehicle wheel brakes and a plurality of hydraulic pressure generators. The wheel brakes may serve as the external devices and the hydraulic pressure generators may serve as the hydraulic fluid supply devices.
Therefore, even when any of the hydraulic pressure generators fail to supply the pressurized fluid to the corresponding pressure chamber(s) due to any troubles, the pressurized hydraulic fluid may be reliably delivered to all of the wheel brakes. In other words, the wheel brakes can reliably apply braking forces to their respective wheels.